SolidColorBrush Opacity property from 1 to 0
<Window x:Class="Workspace.DockExample" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Workspace" Width="640" Height="480"> <StackPanel> <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1" > <Rectangle.Fill> <SolidColorBrush Color="Blue" Opacity="1" /> </Rectangle.Fill> </Rectangle> <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1"> <Rectangle.Fill> <SolidColorBrush Color="Blue" Opacity="0.75" /> </Rectangle.Fill> </Rectangle> <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1"> <Rectangle.Fill> <SolidColorBrush Color="Blue" Opacity="0.5" /> </Rectangle.Fill> </Rectangle> <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1"> <Rectangle.Fill> <SolidColorBrush Color="Blue" Opacity="0.25" /> </Rectangle.Fill> </Rectangle> <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1"> <Rectangle.Fill> <SolidColorBrush Color="Blue" Opacity="0" /> </Rectangle.Fill> </Rectangle> </StackPanel> </Window>